Optimizing nitrogen management with a magnesium supply improves rice yield and nutrient-use efficiency

Abstract

Nitrogen (N) and magnesium (Mg) are essential nutrients that jointly regulate rice growth, productivity, and nutrient utilization, particularly in acidic, Mg-deficient soils. Delayed N application is a key strategy for improving N-use efficiency and achieving N-conserving, yield-stable rice production. However, research on the synergistic effects of delayed N application combined with Mg fertilization on rice growth, yield, and nutrient-use efficiency under the unique plateau climate and Mg-deficient soil conditions of Mianning County in Sichuan Province, China remains limited. We investigated the effects of different N application strategies combined with Mg fertilization on rice yield, biomass production, and nutrient-use efficiency in this high-altitude rice-growing region. A two-year field experiment (2024–2025) was conducted using a split-plot design with the rice cultivar Shenyou Yuehe Simiao. The main plots received a constant N application rate of 150 kg/hm 2 applied at three basal:tillering:panicle ratios (20:20:60–N2:2:6, 30:30:40–N3:3:4, and 40:40:20–N4:4:2), together with a zero-N control. The subplots received Mg at 0, 60, or 90 kg/hm 2 , expressed as Mg0, Mg1, and Mg2, respectively. The assessed parameters included yield components, dry matter accumulation and translocation, N management, Mg fertilization, year, and their interactions, all of which significantly influenced rice growth and nutrient utilization. The combination of the 30:30:40 N application regime with 60 kg Mg/hm 2 consistently achieved the highest grain yield (11,332.7 kg/hm 2 ), representing an 8.7% increase compared with the corresponding treatment without Mg application. At the full heading and maturity stages, dry matter accumulation reached 11,103.38 and 16,286.69 kg/hm 2 , respectively; the amount and rate of dry matter translocation from stems and leaves were 2,745.20 kg/hm 2 and 38.77%, respectively. This combined application significantly promoted N uptake, with total plant N accumulation of 144.38 kg/hm 2 ; agronomic efficiency, partial factor productivity, and recovery efficiency of N fertilization of 21.64 kg/kg, 62.96 kg/kg, and 35.32%, respectively. These findings demonstrate that optimizing N application timing (30:30:40) combined with 60 kg Mg/hm 2 synergistically enhances dry matter accumulation and translocation, nutrient-use efficiency, and carbon metabolism, thereby improving rice grain yield in Mg-deficient soils.